U.S. Pat. No. 4,532,755, which is assigned to the assignee of this application, discloses clipping collection apparatus for cooperation with a rotary mower carried at the underside of a riding vehicle, whereby clippings produced by the mower are conducted through a clipping duct that extends rearwardly and upwardly along one side of the vehicle, from a mower housing clipping outlet opening to that side of the vehicle to a clipping receptacle carried on the rear of the vehicle. In that apparatus the rotary mower blade adjacent to the clipping outlet has relatively large trailing edge lift portions at its tips so that its rotation induces a strong airflow out through the mower housing clipping outlet and rearwardly along the clipping duct. The front portion of the clipping duct is so configured as to cause a minimum of resistance to this airflow and to extend as nearly as possible in the direction of the trajectories of clippings passing through the outlet, so that clippings have little tendency to impact the inner wall surfaces of the clipping duct but are instead carried in an airstream flowing smoothly along the duct. Such constant, non-plugging flow of clippings along the clipping duct is further promoted by the configuration of the discharge portion of the clipping duct and of a cover for the clipping receptacle, which are designed to cooperate in preventing clippings from being substantially decelerated until they are over the part of the clipping receptacle into which they are intended to fall.
This prior apparatus was highly successful with two-spindle rotary mowers but was found not to be satisfactory with threespindle mowers. A three-spindle mower is one that has three cutting blades, mounted on spindles spaced apart transversely to the direction of travel of the mower. In the usual case a three-spindle mower cuts a wider swath than a two-spindle mower but its blades are of smaller radius than those of a two-spindle mower. Because of its smaller tip orbit, the blade adjacent to the clipping outlet of a three-spindle mower is inherently unable to produce the high airflow generated by its counterpart on a two-spindle mower. Nevertheless, the wider swath cut by a three-spindle machine produces a substantially heavier flow of clippings to be propelled through the mower housing clipping outlet and along the duct to the clipping receptacle.
Since a three-spindle mower cannot, by itself, produce a strong enough airflow for satisfactorily propelling its high volume clipping output into the clipping receptacle, a supplementary airflow must be generated by means of an impeller. Several impeller arrangements for this purpose have been proposed heretofore, but every such prior arrangement has had one or more significant disadvantages.
U.S. Pat. No. 4,433,532 discloses apparatus wherein a blower is located at the rear of the vehicle and draws in air from the clipping receptacle, through a screen. Air discharged from the blower is pumped forward through an air tube and is discharged into the front end portion of the clipping duct through a rearwardly opening nozzle that accelerates it to a high velocity. The airstream issuing from the nozzle produces a suction forwardly of the nozzle whereby air is drawn out of the mower housing, and to the rear of the nozzle the discharged air accelerates the flow of clippings along the clipping duct. The presence of the blower tends to reduce the capacity of the clipping receptacle, but a more significant disadvantage of this arrangement is that the air tube and the clipping duct constitute a rather cumbersome and expensive assembly. Their connection must be maintained under the rather severe vibration to which mowing apparatus is subjected but must nevertheless be readily disconnectable. There is also a possibility that the apparatus would not operate well under all conditions, since the air discharge nozzle in the clipping duct presents a surface against which clippings tend to impact and upon which they are therefore likely to build up into a plug that would block the clipping duct and defeat the purpose of the blower.
Each of U.S. Pat. Nos. 3,037,339 and 3,657,865 discloses a paddle-vane impeller at the discharge side of a mower housing, rotating on a horizontal axis and intended to impart a rearward and upward acceleration to clippings issuing from the mower housing discharge outlet. An obvious disadvantage of these devices is that the bulky impeller projects both laterally beyond the mower housing and to a substantial height above it and thus interferes with mowing along a row of lowgrowing bushes or in a similar confined space. Furthermore, a relatively complicated 90.degree. transmission is needed for driving such an impeller, since its axis is at right angles to the upright mower blade spindles.
U.S. Pat. No. 4,114,353 discloses a paddle-vane impeller mounted outwardly adjacent to the mower housing clipping outlet of a three-spindle mower, rotating on a vertical axis and situated in approximately the plane of the cutting blades, to receive the clippings issuing from the clipping outlet and propel them rearwardly towards a receptacle. This arrangement also interferes with mowing in confined spaces because the impeller has its entire diameter at one side of the swath cut by the mower blades. Furthermore, the size of the clipping outlet tends to be effectively restricted by the impeller unless it has a relatively large diameter, since the impeller vanes are effective to draw clippings out of the mower housing only in the quadrant of their orbit in which they are nearest the mower blades and moving away from them.
U.S. Pat. Nos. 2,920,435 and 3,065,588 disclose single-spindle mowers, each having its clipping outlet centered in the rear portion of its mower housing and having an impeller mounted over the clipping outlet to draw clippings out of the housing and propel them rearward into a receptacle. Such an arrangement is obviously suitable only for a single-spindle mower and therefore offers no suggestion that could be usefully applied to a multi-spindle mower, which must have a sidewardly opening clipping outlet.
U.S. Pat. Nos. 4,361,000 and 4,407,112 disclose single-spindle rotary mowers wherein a blower is mounted above the cutting blade, concentrically with its spindle and driven by that spindle. The housing of a multiple-spindle mower could not be formed to accommodate the air flow pattern intended to be produced by such a coaxial blower; hence these patents offer no suggestion for solving a problem that is peculiar to apparatus comprising a three-spindle mower.
One arrangement employed with a three-spindle mower is illustrated generally by U.S. Pat. No. 4,104,852, wherein a vacuum-producing blower is mounted on the rear of the riding vehicle that carries the mower and is driven from the power takeoff on that vehicle. The clipping duct leads rearwardly from the mower clipping outlet to the intake of the blower, and the blower discharges rearwardly into a clipping receptacle that is carried on the vehicle by means of rearwardly projecting brackets. The blower and the clipping receptacle thus function in essentially the same manner as a vacuum sweeper. Although generally satisfactory, this apparatus is not completely trouble-free with wet or juicy clippings because they must undergo successive abrupt changes of direction in the course of flow to and through the blower.
Since the blower in the last described apparatus must pump a substantially high volume of air in order to produce enough vacuum to suck clippings into it, it draws a substantial amount of power from the vehicle engine, which must also power the mower and propel the vehicle. In a commonly used variant of this expedient, therefore, the blower and the clipping receptacle are carried by a trailer cart that is towed behind the mower-carrying vehicle, and the blower is powered by an engine mounted on that cart. From the functional standpoint this is perhaps the most satisfactory clipping collection apparatus heretofore devised for cooperation with a three-spindle mower, but it is obviously expensive because of the separate engine needed for powering the blower, together with the trailer chassis needed for carrying that engine, the blower and the clipping receptacle. Because of the additional engine this apparatus is relatively noisy in operation. The requirement for towing a trailer is also a disadvantage because it decreases the maneuverability of the mower.
From the foregoing review of the prior art, it will be apparent that there has been a long-standing unsatisfied need for simple, compact, inexpensive and functionally satisfactory clipping collection apparatus suitable for cooperation with a three-spindle mower carried at the underside of a riding vehicle and whereby clippings produced by the mower are reliably propelled away from the sidewardly opening discharge outlet in the mower housing and are driven into a clipping receptacle at the rear of the vehicle. It will also be apparent from the foregoing discussion that the problem of satisfying this need is a complicated one that poses numerous requirements.